1. Field of the Invention
This invention relates to a thermoelectric conversion apparatus, which converts thermal energy to electrical energy.
2. Description of Related Art
In recent years, attention has been given to thermoelectric conversion systems containing heat regenerative type fuel cells as thermoelectric conversion apparatuses that recover heat at comparatively low temperatures (referred to hereunder as low grade heat), up to approximately 100° C. for example, and convert it to electrical energy (refer to patent reference 1 and patent reference 2).
In these thermoelectric conversion systems, thermal energy is supplied to induce an endothermic dehydrogenation reaction in a particular type of organic compound on a catalyst, and hydrogen and dehydrogenated substances (referred to hereunder as dehydrogenated substances), which are produced by this reaction, and hydrogen are reacted (hydrogenation reaction) electro-chemically to recover electrical energy. In such a thermoelectric conversion system, since there is no thermodynamic restriction (Carnot efficiency), a highthermoelectric conversion efficiency can be expected.
For example, in a case where acetone, being a dehydrogenated substance, undergoes a hydrogenation reaction to create isopropyl alcohol (abbreviated hereunder as IPA), its reaction equation is represented as equation (1)(CH3)2CO→H2+(CH3)2CHOH  (1)
Here, when the operating temperature is 25° C., the value of the enthalpy variation ΔH=−55.5 kJ/mol, and the Gibbs free energy variation ΔG=27.5 kJ/mol. Therefore, the thermoelectric conversion efficiency η is η=ΔG/ΔH=49.5%.
Patent Reference 1: Japanese Patent No. 1-25972.
Patent Reference 2: Japanese Unexamined Patent Application, First Publication No. 2002-208430.
In actual usage, considering for example the temperature of waste heat to be applied as thermal energy to induce an endothermic dehydrogenation reaction, or the activation temperature of a catalyst to induce an endothermic dehydrogenation reaction, it is necessary to operate at around 100° C. However, in the case where the operating temperature is 100° C., since the value of the enthalpy variation ΔH=−56.4 kJ/mol, and the Gibbs free energy variation ΔG=12.2 kJ/mol, the thermoelectric conversion efficiency η is η=ΔG/Δ=21.6%, which is lower than the 100° C. Cannot efficiency (29.8%).